A power system is configured with many generators, a load, a transmission and distribution device, and a control device. In a normal state, minute disturbance caused due to a variation in a load or switch of a system is added to an electric power system. When an accident such as a ground fault or short-circuit of a system occurs, large disturbance is added to an electric power system. Electric power fluctuation having a plurality of fluctuation components occurs due to such disturbance.
In a case in which the fluctuation mode component is small or is attenuated at a high speed, system fluctuation is maintained in a sufficiently small range after the occurrence of the disturbance. Therefore, the electric power system is in a stable state. However, in a case in which the fluctuation increases or the attenuation continues or diverges without convergence, an electric power generator consequently stops or a wide-area power failure occurs, and thus there is a possibility of a stable operation being unfeasible.
With expansion of an electric power system scale, there is a tendency that an electric capacity increases, a remote area is distant, maldistribution increases, power transmission lines increase with the maldistribution, and double-flow progresses. Since an influence of such changes is exerted in a direction in which stability of a power system deteriorates, there is a concern of a successive influence expanding to large-scale power falling and wide-area power failure originating due to step-out of an electric power generator at the time of breakdown of the system.
Therefore, an online system stability evaluation method of previously preventing and predicting involvement in the wide-area power failure by normally monitoring stability of the system is necessary.
In recent years, a phase detector PMU (Phasor Measurement Unit) measuring a bus voltage phase angle of an electric power system in substantially real time by performing synchronization measurement using the global positioning system (GPS) has spread. A power fluctuation phenomenon can be ascertained in real time using an online measurement value such as a system bus voltage measured by the phase detector PMU.
However, a deficient value or an abnormal value is included in a PMU measurement value due to a measurement device failure, communication delay, or the like. There is a possibility that a monitoring result deviated from an actual system state is output as a system state monitoring result obtained using the PMU measurement value including a deficient value or an abnormal value. When a control policy of the power system is decided using an inaccurate state monitoring result, unnecessary control is performed or stability of a system deteriorates as a result, and thus there is a possibility of a large-scale power failure being involved.
In regard to the foregoing problems, state estimation has been known. For example, PTL 1 discloses “a power system calculator system monitoring and controlling an electric power system and including: a collection unit that collects data of each unit of the electric power system; a state estimation unit that estimates magnitudes and phase angles of all the bus voltages of the electric power system which are most probable on the basis of the collected data and requests any one of an effective or ineffective electric power flow of an entire system, an effective or ineffective power injection amount of the entire system, and apparent power on the basis of the estimated magnitudes and phase angles of the bus voltages; a system monitoring processing unit that monitors an electric power system state on the basis of estimation result data in the state estimation unit and stores the electric power system state in an online database; and various processing functions of performing various processes using data stored in the online database”.